The use of p-aramid, carbon and glass fiber in the reinforcement of organic polymer matrices of composites is disclosed in U.S. Pat. No. 4,511,690 and other prior art. Fiber surface coatings are also prescribed in some prior art to either enhance or diminish the adhesion of the matrix material to the fibrous reinforcement. A combination of fiber, fiber coating and matrix has now been found which greatly improves the level of flex fatigue life of composites well beyond that exhibited in the absence of the fiber coating. This quality is of importance in end uses, such as axles, aircraft wings, and automotive leaf springs.